It is well known that vehicle drivers frequently underestimate the force of water flowing across a low water crossing. During floods, news reports are replete with situations where otherwise rational people drive across a low water crossing only to be stranded in the road or swept downstream by flowing water. Sometimes these situations end in disaster, sometimes rescue personnel risk their safety and lives to rescue the drivers and occupants of vehicles.
Governmental authorities in flood prone areas have typically responded to this situation by sending police or firemen to place standard traffic barricades in the road adjacent low water crossings. These barricades must be placed in a timely manner at appropriate locations, must be sufficient in size and placement to deter motorists and must be monitored to prevent the barricades from being moved or removed by motorists or flood water.
The failures of current techniques are in categories that match up with the requirements of effective barricades, i.e. they are not placed in a timely manner, they are not placed at appropriate low water crossings or are inappropriately positioned at proper low water crossings, motorists drive around or move barricades and flood waters turn barricades over or sweep them downstream. There is accordingly no dispute that current techniques are inadequate, the most persuasive evidence being motorists stranded in the road or swept downstream during floods.
There are many types of indicators or alarms that have been proposed or used to show attentive motorists that water has risen and by how much. The simplest and most widely used is a piece of pipe embedded in the ground near a low water crossing with marks on the pipe showing the height of water flowing over the road. A number of proposals have been made for alarms or indicators placed on the side of the road, which are actuated by rising water, to indicate that the water height is dangerous such as shown in U.S. Pat. Nos. 2,607,835 and 4,879,545. Other disclosures of interest are found in U.S. Pat. Nos. 4,377,352; 5,460,462; 5,862,775 and 6,623,209.